Gastric type H+,K+-ATPase in the cochlear lateral wall is critically involved in formation of the endocochlear potential

Cochlear endolymph has a highly positive potential of approximately +80 mV known as the endocochlear potential (EP). The EP is essential for hearing and is maintained by K⁺ circulation from perilymph to endolymph through the cochlear lateral wall. Various K⁺ transport apparatuses such as the Na⁺,K⁺-ATPase, the Na⁺-K⁺-2Cl^– cotransporter, and the K⁺ channels Kir4.1 and KCNQ1/KCNE1 are expressed in the lateral wall and are known to play indispensable roles in cochlear K⁺ circulation. The gastric type of the H⁺,K⁺-ATPase was also shown to be expressed in the cochlear lateral wall (Lecain E, Robert JC, Thomas A, and Tran Ba Huy P. Hear Res 149: 147–154, 2000), but its functional role has not been well studied. In this study we examined the precise localization of H⁺,K⁺-ATPase in the cochlea and its involvement in formation of EP. RT-PCR analysis showed that the cochlea expressed mRNAs of gastric ₁-, but not colonic ₂-, and -subunits of H⁺,K⁺-ATPase. Immunolabeling of an antibody specific to the ₁ subunit was detected in type II, IV, and V fibrocytes distributed in the spiral ligament of the lateral wall and in the spiral limbus. Strong immunoreactivity was also found in the stria vascularis. Immunoelectron microscopic examination exhibited that the H⁺,K⁺-ATPase was localized exclusively at the basolateral site of strial marginal cells. Application of Sch-28080, a specific inhibitor of gastric H⁺,K⁺-ATPase, to the spiral ligament as well as to the stria vascularis caused prominent reduction of EP. These results may imply that the H⁺,K⁺-ATPase in the cochlear lateral wall is crucial for K⁺ circulation and thus plays a critical role in generation of EP. hydrogen, potassium-adenosine triphosphatase; stria vascularis; spiral ligament